Your daughter is being very naive, but she IS an adult.
Insist on speaking to him and his family on skype with her.
Get his address off of them and ask them to describe what the road is like. Fucking google earth it to check if they are being honest. Get their home phone number. Try calling it whilst still on skype so you can see if it's the right one or not.
Get the number of the british embassy and tell you daughter that if she has not rung you by a certain time, every single day, you will be calling the embassy immediately to report her as missing, and giving her friends name as prime suspect.
If she doesn't want to face this abject humiliation, then she is to FUCKING RING YOU.
Insist that she takes well hidden cash, and no cards. That way her cards can't get nicked (I've been to Romania. There is a fuck ton of pick pocketing).
Insist she is to stay in a hotel, and book it if you can. There aren't many decent hotels in the capital, and the decent ones are pretty expensive.